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  3. Is Earth Getting Warmer? The National Academy of Sciences claimed recently that people should caution rather than panic about th

Is Earth Getting Warmer? The National Academy of Sciences claimed recently that people should caution rather than panic about th

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问题                         Is Earth Getting Warmer?
The National Academy of Sciences claimed recently that people should caution rather than panic about the greenhouse effect. It is said that the greenhouse effect will result in global warming, which will elevate the earth’s temperature by 3~9 degrees Fahrenheit. The greenhouse effect results when carbon dioxide(CO2)and certain other gases in the atmosphere allow the sun’s ultraviolet rays to penetrate and warm the earth, but then absorb the infrared energy the earth radiates back into space- much as glass in a greenhouse does—forming a kind of "thermal blanket" around the planet. The greenhouse effect will mean much more than hotter summers and milder winters. It may alter rainfall, affect crop yields and eventually—as glaciers begin to melt—raise the level of the seas. It had long been reported that the earth’s temperature would rise, melting the icecaps, raising the seas, flooding the land. Half of Long Island would be under water. Midwest would become a desert. However, the findings of latest studies have indicated that the earth might not undergo warmer temperatures and rather it may experience colder weather.
    Due to the variable behavior of the sun, the earth may be confronted with another Ice Age. In the past, concern about a man-made warming of the earth has concentrated on the Arctic because the Antarctic is much colder and has a much thicker ice sheet. But the weather experts are now paying more attention to West Antarctic, which may be affected by only a few degrees of warming: in other words, by a warming on the scale that will possibly take place in the next fifty years from the burning of fuels.(A)Satellite pictures show that large areas of Antarctic ice are already disappearing.(B)The evidence available suggests that a warming has taken place. This fits the theory that carbon dioxide warms the earth.(C)Scientists conclude, therefore, that up to now natural influences on the weather have exceeded those caused by man. The question is: Which natural cause has most effect on the weather?(D)
    One possibility is the variable behavior of the sun. Astronomers at one research station have studied the hot spots and "cold" spots(that is, the relatively less hot spots)on the sun. As the sun rotates, every 27. 5 days, it presents hotter or "colder" faces to the earth, and different aspects to different parts of the earth. This seems to have a considerable effect on the distribution of the earth’s atmospheric pressure, and consequently on wind circulation, The sun is also variable over a long term: its heat output goes up and down in cycles, the latest trend being downward. Scientists are now finding mutual relations between models of solar-weather interactions and the actual climate over many thousands of years, including the last Ice Age. The problem is that the models are predicting that the world should be entering a new Ice Age and it is not. One way of solving this theoretical difficulty is to assume a delay of thousands of years while the solar effects overcome the inertia of the earth’s climate. If this is right, the warming effect of carbon dioxide might thus be serving as a useful counterbalance to the sun’s diminishing heat.
    In addition to the variable behavior of the sun, new research has also demonstrated that global warming will probably lead in the end to a period of much colder weather, at least in Europe. Scientists base their theory on what happened the last time the world warmed up, 8 300 years ago. They have discovered that when the ice melted from the northern polar ice cap it became trapped in an enormous lake in northern Canada. As more ice melted this lake suddenly burst open, releasing millions of tons of freezing fresh water into the North Atlantic. This flood of water was so large that it prevented the normal flow of water in the Atlantic, which takes warm water from the tropics north to Europe and thus temperatures in Europe dropped by between three and eight degrees Celsius over the next two hundred years. Scientists believe that a similar process could occur in the next century if the Greenland Ice Sheet starts to melt.
An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.
The latest research demonstrates that the earth may experience colder weather in the future.

                        Answer Choices
(A)The ice melting from the northern polar ice cap 8 300 years ago leads to the release of millions of tons of water from a lake into the North Atlantic.
(B)The behavior of the sun has more effect on the weather of the earth than greenhouse effect caused by man’s burning of fuels.
(C)Since the sun’s heat output is going down at present, scientists claim that the earth is likely to experience cold temperature thousands of years in the future.
(D)Greenhouse effect might not do harm to humans and rather may bring benefits to human beings.
(E)It is pointed out that humans’ burning of fuels will eventually cause the ice sheet in the polar areas to melt and thus flood the whole earth.
(F)The facts of the last Ice Age show that the earth may undergo much colder weather in the next century if the Greenland Ice Sheet begins to melt.
选项
答案B. The behavior of the sun has more effect on the weather of the earth than greenhouse effect caused by man’s burning of fuels. C. Since the sun’s heat output is going down at present, scientists claim that the earth is likely to experience cold temperature thousands of years in the future. F. The facts of the last Ice Age show that earth may undergo much colder weather in the next century if the Greenland Ice Sheet begins to melt.
解析 本题为篇章总结题，考查考生掌握全篇中心思想和相关重要信息的能力，要求考生能够区分主要观点、次要观点以及文章中没有提及的观点，以达到总结全篇的目的。本文主要阐述地球变冷的原因。选项B、C、F正是文章对第二、三、四段内容的总结句，所以选B、C、F。
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